1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly, to a method for fabricating a semiconductor device in which etching by-product is deposited on a photoresist film used as a mask.
2. Discussion of the Related Art
In a logic device, particularly, a flash memory device, the higher the packing density of the device, the smaller the Critical Dimension (CD) becomes. Consequently, if a floating gate pattern of the critical dimension below 130 nm is to be formed, not only the critical dimension of the gate pattern, but also the critical dimension of a space between adjacent gate lines becomes smaller, i.e. below 100 nm.
This requires reducing the thickness of the photoresist film to match the depth of focus of a KrF light source of a 248 nm wavelength. However, a balance must be achieved between reducing the thickness of the photoresist film for matching a depth of focus and maintaining a minimum required thickness of the photoresist film for etching. If the proper thickness of the photoresist film is not obtained, a defective pattern, such as deformation, or collapse of the pattern, is likely to happen.
To solve this problem, instead of using a KrF light source, an ArF light source of a 193 nm wavelength can be used in fabrication of a polysilicon transistor. However, since the critical dimension of a space between adjacent gate patterns is below 100 nm, the fabrication of the polysilicon transistor is difficult and takes a long time.
Following is a description of a method for fabricating a semiconductor device of a micronite pattern by using the KrF light source in accordance with the related art. The related art method for fabricating a semiconductor device will be described with reference to the attached drawings.
FIGS. 1A-1G illustrate sectional views of a semiconductor device as it is fabricated according to a method of the related art.
Referring to FIG. 1A, a gate insulating film 11, a polysilicon layer 12, a first insulating film 13, and a Bottom Anti-Reflection Coating (BARC) 14 are deposited on an entire surface of a substrate 10. The BARC serves for preventing a standing wave from occurring, in which a light passed through a photoresist film and interfers with a light reflected by the wafer during an exposure step thereby impairing the formation of a pattern profile after exposure and development of the photoresist film.
A photoresist film is coated on an entire surface of the substrate 10 including the BARC 14, and subjected to selective exposure and development, to form a photoresist film pattern 15.
Referring to FIG. 1B, the photoresist film pattern 15 is used as a mask for the selective removal of the BARC 14, to form a BARC pattern 14a. 
Referring to FIG. 1C, the photoresist film pattern 15 is also used as a mask for etching the underlying first insulating film 13, to form a first insulating film pattern 13a. 
Referring to FIG. 1D, a second insulating film 16 is formed on an entire surface of the polysilicon layer 12 including the insulating film pattern 13a. 
Referring to FIG. 1E, an etch-back of the second insulating film 16 is performed to form sidewall spacers 16a at sidewalls of the first insulating film pattern 13a. The etch-back is an anisotropic etching of flat surfaces so that, in FIG. 1E, the second insulating film 16 is removed completely from an upper side of the polysilicon layer 12 and an upper side of the first insulating film pattern 13a, both of which are the flat surfaces, while only slightly removed from an upper side of sidewalls of the first insulating film pattern 13a, thereby leaving a portion of the second insulating film 16 even after the etching.
Referring to FIG. 1F, the first insulating film pattern 13a and the opposite sidewall spacers 16a are used as a mask for etching the polysilicon layer 12, to form a polysilicon pattern 12a. 
Referring to FIG. 1G, the first insulating film pattern 13a and the sidewall spacers 16a left on the polysilicon pattern 12a are removed.
The polysilicon pattern 12a formed in this manner is used as a gate line or a gate electrode. The related art method for fabricating a semiconductor device suffers from poor process yield caused by repetitive and complicate deposition and etching steps, and contamination with defects caused by the use of many apparatuses coming from the repetitive, and complicated deposition and etching processes.
Additionally, the related art method uses an oxide hard mask to form a gate pattern with a line to line space critical dimension of below 100 nm.
Repetitive etching and film deposition as done in the related art complicate the fabrication process, require many apparatuses, and have a poor process yield caused by the contamination defects.